As a result of examining Hittite Verbs at the different chronological stages the following two conclusions have been obtained.1.While Proto-Anatolian ^<**>'-eN# became-aN# in Hittite, ^<**>-eN# remained intact. This sound change provides a reliable source which acted as a locus from which the 1 pl.preterite-wen and 2 pl.-ten were generalized. Why this generalization was regular while neither-wani or-tani was completely ousted in the historical period of Hittite is due to the pressure of the vocalism of the 3 pl.present-anzi and 3 pl.preterite-er.2.Both^<**>-ti and ^<**>-di underwent assibilation at a pre-Hittie stage ; the ending-Izzi with zzreflects pre-Hittite ^<**>-ti and -i/ezi with z reflects pre-Hittite ^<**>-di. A small number of Old Hittite verbs such asi-e-zi "does" KBoVI2I60 preserve a notably archaic feature, resisting to generalization of -Izzi with zz. Unlike ^<**>t and ^<**>d, Proto-Indo-European voiced aspirate ^<**>dh never got assibilated in Hittite. Consequently, Proto-Indo-European and ^*d and ^<**>dh show different outcomes before ^<**>i in Hittite. This will be a piece of evidence for a view that Proto-Indo-European ^<**>d and ^<**>dh had not been merged at the stage of Proto-Anatolian.